Highly Efficient PVDF‐HFP/Colloidal Alumina Composite Separator for High‐Temperature Lithium‐Ion Batteries

Abstract

Toward high‐temperature lithium‐ion batteries, adding inorganic materials are proposed as an effective strategy. However, inorganic particles tend to aggregate in the polymer matrix, causing degradation in battery performance. Here, a PVDF‐HFP/colloidal Al2O3 composite separator is prepared with a phase inverse method. The colloidal Al2O3 particles well dispersed in the PVDF‐HFP polymer matrix substantially enhance the mechanical strength of the PVDF‐HFP separator. The PVDF‐HFP/colloidal Al2O3 composite separator owns a high electrolyte uptake of 372%, a high ionic conductivity of 1.3 × 10−3 S cm−1 at 80 °C and delivers high capacity retention of 95.6% after 100 charge–discharge cycles at 0.5 C. In addition, PVDF‐HFP/colloidal Al2O3 separator only has a 4.5% thermal shrinkage at 150 °C and exhibits high electrochemical performances upon annealing at 140 °C.

Recent Development in Separators for High‐Temperature Lithium‐Ion Batteries

“…The LFP/Li batteries based on PVDF‐HFP/colloidal‐TiO 2 separator deliver remarkable discharge capacity at elevated temperatures, as given in Figure e,f. Similarly, Ali et al reported the same concept as reported by Waqas et al of using colloidal oxide as a filler with PVDF‐HFP to ensure the uniformity but they used bisolvent dissolution method for fabrication of PVDF‐HFP/colloidal Al 2 O 3 composite separator. The use of two different solvents increases the porosity with a uniform microporous structure due to the variation in evaporation rate of solvents, as shown in Figure g.…”

“…However, for high electrochemical performances, the separator should be thin with high porosity for efficient transport of lithium‐ions. Therefore, for increasing the mechanical strength, the thickness of separator must be increased, while by increasing the thickness of separator, the ionic conductivity and lithium‐ion transference number decrease, which effects the electrochemical performances . Therefore, on a practical level, the separator should own appropriate properties in order to achieve high electrochemical performances and ensure the safety as well.…”

“…g) SEM image of PVDF‐HFP/C‐Al 2 O 3 separator showing highly porous structure, h) tensile strength graph, and i) thermal shrinkage graph of PVDF‐HFP and PVDF‐HFP/C‐Al 2 O 3 separators. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

“…However, at high‐temperatures, the LIBs depict abnormal performances due to the decomposition of lithium salts present in the electrolyte, low thermal stability of separators, and instability of electrodes. The high temperatures introduce thermal fluctuations inside batteries during the charge–discharge process, which results in internal short circuits and leading to thermal runaway and fire explosion . Many incidents have been reported recently regarding the fire explosion of LIBs mainly caused by the internal short circuits and thermal runaway.…”

Uniform Lithium Nucleation Guided by Atomically Dispersed Lithiophilic CoNx Sites for Safe Lithium Metal Batteries

“…Remarkable achievements have been achieved to address these issues involved in Li metal anodes, including exploiting electrolyte additives to construct stable SEI films, designing high‐modulus solid/composite electrolytes to impede dendrite penetration, and engineering stable artificial interfacial layers to inhibit dendrite growth . However, the relatively infinite volume change induced by the hostless feature of Li plating/stripping at a high areal capacity is a formidable challenge.…”